Regulator for electric motors



(N0 Model.)

N. EI REGULATORP LEG MOTORS.

No..4161.69. Pateuted Den. 3, 1889.

UNITED STATES PATENT OFFICE.

NATHANIEL SI-IEPARD KEITH, OB SAN FRANCISCO, CALIFORNIA.

REGULATOR FOR ELECTRIC MOTORS.

SI E CIFICATION forming part of Letters Patent N0. 416,169, datedDecernber 3, 1889. Application fi1ed December 24, 1888. Serial N0.2944='76. (N model.)

T0 all wh0m it may co7wern:

Be it known that I, NATHANIEL SHEPARD KEITH, a citizen of the UnitedStates, and a resident of San Francisco, in the counuy of San Franciscoand State of California, have y inventd certain newand usefnlImprovements in Eleotrio Motors, of which the fo11owing is aspecifioation.

My invention oonsists in so oonstituting a dyna1no-eleotrio maohine,when used as an electrio 11101301, (hat io 1nay be p1aoed in series withone 01' more electrio motors of ehe sa1ne 01 other kin'd. upon a circuitsupplied With an approxirnately oonstant ourrent in ampres, and run aban approximately oonstant speed with the 1naximnm of eflioienoy.

Parts of my inven'oion may also be nsed 011 e1eotric motors otherwiseoonstituted, as is hereinafter n1o1e ful1y set fo1th.

I is we1l known thao the torque ('ohe turning moment) of an electriomotor is dependent in a g1eat n1easure, other things being eqnalupo uthe magnetio strengch of its fieldmagnetif it be strong, the 1110to1 isstrong; if it be weak, the motor is weak. The govemment of the speed ofn1otors nnder varying 1oads has been acoomplished more 01 1essin1pe1feotly by varying in many ways the strength of magnetisxn of theirfield-rnagnets.

I is well-known that the true 1ine of 00111- 1nntation on theoomrn'utator of a dynamoeleotrio maehine shiftswith variations 111 therelative strenghs of n1agnetism of its ar1nature and field-magnets. Ifthe field-magnet be ext-remely strong, the Urne line of 0011111111- tation is near1y coinoident With a plane 1111dway bet-ween 1311e po1es ofits field-magnet;

but if he field-1nagnet be weaker the true 1ine of oommutauion is n1ovedin the direction toward a position at right an g1es thereto. If thefield-1nagnet be extren1ely weak, the true line of com1nutation isnearly ooinoident 1vith a line drawn at right angles to a planesituatedmidway between the po1es of its field- 1nagnet. In the oase of adynamo-eleotrio maohine used as a generator of eleet1ioit3 on weakeningthe field-magnet the true 1ine of .comn1utation moves in t-he direetion01: the rotation of its armacure. I have demonstrated in praotioe thatin the case of a dynamo-electrie 1n1ohine used as an e1eotric 1noto1,011 weakening the field n1agnet the true 1ine of oo1nmutation rnovesreversely to the direetion of the rotation of its a1n1ature.

Tl1e maximu1n torque of an eleortio motor is exerte'd when the brushesbea1 upon t11e oomn1utator 011 the 1ine ooexistent with a plane midwaybetween the po1es of its fieldmagnet. line 011 the 'oiroun1ferentialplane of the commutator, tl1e torque Will be 1ess as the 1110Ve mentprogresses, unnil when they a1e 011 the 1ine ooexistent With a 1inedrawn a rigl1t ang1es to a plane situated midway between the poles ofits field-magnets 113 W i11 entirely eease.

The torque 0f a series-wound electric 1110- to1 has been varied toaooord With the 1ne ohanioal resistance whioh 113 overoame, 111 order tokeep its speed of rotation as near1y uniform as possible, by varyin g1she position of oont-aco of its brushes 011 its oon1mutator. This is awasceful way, beoause the electrio If the brushes be 1noved f10111 that1 resistanoe of tl1e 1notor ren1ains the san1eand unde1 s111a11 loadsthe energy used in overooming this resistance is a very large peroentageof the total energy given to the 1110- tor. I1; is also destruooive ofbrushes and 001111n utato1 by reason of the exoessive spark 111g attheir points of oontaot, due to these points being away f10111 tl1e trueline of commutation.

The torque of a series-wound electrio motor has been varied 130 aecordwitah the mechanica1 resistanoe whicl1 113 overoan1e, in Order to keepits speed of rotation as nearly uniform as possible byvarying tl1ea1np(re-turns of its field-magnet in several ways. \Vhen ohis has beendone by automatio n1eans, the brushes have 11013 beon moved Co t-l1eposition 11 111011- aeeords with ehe line of con11nntation due to t-heohanged magnetism of oho field-magnets; therefore injurious spa1king atoo1nrnntatorbrush oontaots took p1ace.

By his n1y invention 1 provide 111ea11s whereby so1ne of thesel1ereinbeforestated and tear due t0 im perfeet 00111 m utati0n,Sparking, &e. 1

Shuntwouncl electric n1otors have been used 0n circuits suppliecl Witl1eleetricity at constant potential, bu l1ave been hitherto inapplicablet0 eonstant-cu rren1: eirenits fron1 reasons 0f inability 10 governtheir speed when on such circuits, general ineflieieney, &e. By this 1nyinvention I put t0 use shuntwound electrie motors having qnalities ofhigh eflicieney, perfeet control 0f speed, an(l 0ther desirablequalifications.

011 the acco1npanying drawings, Figure l 1's an end view,perpencliexlla'r t0 the armature-shaft 0f an electrie n1otor, 0f adevice whieh I have usecl in carrying 0ut 1nyinvention. Fig. 2 is alongitudinal secti0nal view 0f thesame, and Fig. 3 is a detail showingm01e plaihly ancl enlarged s0me 0f the parts.

Like lettersof reference in each figure refer t0 like:parts.

A is the shaftof a 1110t01. Securely fastened t0 the shaft, so as t0r0tate with in, is th-e governor=clrum B. In this drun1 are thegov6rnor-w0ights C C, 1vhieh are piv0ted ab D Dso hattheyn1ay-swingthereon. These wei-ghts are *drawn toward eaeh 0Lher bytl1e spiral springs E E. One end 0f eaeh0f the springs is f&astenecl t0the ring R,which spai1s the shaft A, F1 g. Tl1e other ends have nutsfasten'ecl'to tl1em, so that the screws P may be used in adj ustingtheir'tension. The weights O C 11ress,byreason 0f the springs, 0n tl1eperiphery 0f the cylinder G. This eylinder is 1nountecl 011 tl1e bossII, so that it may easily rotaue there0n and concentric witl1 the shafoA. Tl1e cylincler has the arn1s I I, Whi0h carry Ehe brush-holclers J J,and whieh latter hold the brushes -K K. 'lhe brushes in1pinge 011 the00111111110ato1, as usual. T0 the cylinder is attaehed tl1e spiralspring M, which se'rves hyits tension t0 1nove the cylincler and brushesin the reverse direction t0 the n1ove n1ent of the connnutator.

The direction 0f rotation 0f tl1e arn1atu're, commutator, shaft A, anddrum Bis sh0wn by -the arrow in Fig. l. 'Jhis move1nent eauses 131160ylinclenG t0 m0ve in he san1e dire0ti0n, b'y reason 0f fhe pressure 0fthe weights O C 011 the periphery 0f tl1eeylinder G, until ib eomesagainst a stop, (no shown,) but fixed at a point ab which the brushesare causecl t0 bear0n the comn1utator 011 the line, coexistent Witl1 aplane situaiecl n1iclway between th(e:poles 0f its fielcl-1nagnet. Ifthe weights O O d0 not bear 011 the ey1incler G, then tl1e spring M Willeither retain tl1e cylinder in the position ab whicl1 the brushes Willbear 011 the commutator 011 the Ihre dra1vn at right angles t0 the planemiclway between the poles, 01 will return it L0 that p0sition if it hasbefore been movecl fro1n i'm. \Vhen nhe n1otor starts, the brushes Willbe moved forward' to the stop; but as soon as it has aequired suflicientvelocity the weights C O will, fro1n centrifugal force, 1nove slightlyaway from tl1e cylinder G, so that Ehe spring M 1nay pull tl1e cylinder,ar1ns I I, and b1ushes K K backward until the position and speed areattainecl ab which the tension of the spring is exaetly balanced by thefrieti0n 0f ihe weights 0n nl1e cylinder. This will be When tl1eeentrifugal force due t0 tl1e veloeity is just suflieient t0 deereasethe pressure of the weights 011 the cylinder enough t0 reduee theirfrictional contacts therewith to the point ab whieh it balauces thetension of tl1e spring. I prefer 110 cover tl1e eylinderwhere eheWeights impinge 011 it With leather 01 like material wl1ich Will hold0il as a lubricann. I prefer to n1ake the weights C C 0fsteel,phosphor-bronze, or like hard 1naerial, 0r t0 face the1n Withshoes O O, Fig. 3, whieh can be reaclily replaced fron1 time t0 tin1e,as needecl. The lubricated leather-ancl n'1etal surfaees last a l0ngtime 'without reneival.

It is evident thao a sligl1-t recluetion in IO speed 0f rotaionof the-1n0tors armat ureshafo Will cause the weight-s t0 grip tl1e (zylindermore tightly and carry the brushes forward, while a sligl1t increaseWill cause -tl1en1 to loosen their grip son1ewhat, so that thespring'will carry he brushes baekward. I-Ie'retofore lt 11as beenthepractice in regu- 'lating the speecl 0f an eleetric 11101501 t0 moveits brushes frorn the neutral line in thediree- 'ti0n 0f the rotation 0fits armature to (leerease tl1e speed or torque, or both; and towarcl theline in the opposite direetion to increase the speed 01 torque, 01 both.By 1ny 'invention I move the brushes fro1'n Ehe sa1'ne line anal to it,but; intontrary directions, f0r like-governing effecfs, beeause I havef0und that 10 be in praetiee the true Way toavoid undue sparking ab thecon1n1utaiorthat is (so say, wl1en tl1e speed inereasesthe governing;device m0ves the brushes in thedirecl1i011 fron1 the neutral line, butoppo'site t0 the direction 0f rotation 0f tl1e armature 0f the 1notor,and when the speed decreases ehe governing device moves the brushestowar l "the neutral line in the sa1ne direetion as the 'rotati0n 0f thearmature. This is donebecause in an electri0 motor tl1e dist0rtion 0fthe lines 0f force 0f tl1e field-magnet is in tl1e reverse direetionfr01n Lhat 0f an. electric generator.

I prefer t0 Wind the field=1nagnet 0f my 1110- torwith finewire ancleonnect it; after1jheplan 0f a shunt-wound dynan1o. In an eleetricn1otor uncler 1110ti0n, when tl1e brushes bear 011 the connnutatorontl1e plane midway'between the p0les 0f i.ts fielcl-1nagnet,thediiference 0f p0tential 0f t-l1e brushes is at itsmaxi- 11111111,When tl1ey bear 011 tl1e commutator 011 tl1e line at '1iglit angles 1 0tl1e plane, tl1e difference 0f potential 0f tl1e brushesis ab itsmini1nun1. At allpositions 0f the brushes betw aen these two just namedthe clilference 0f potential is 1n0re than when at tl1e latter an(l lessthan when at the formen s0n1ewhaf; in proportion t0 th e distance afiwhicl1 the brushes are fro1n these lines. It is evident, then, that IOOIIO

Wifll a shunt-wound motor whose field-magne'o coils are derived ab thebrushes the position of the brushes when ohe arme/eure is in 1110- tion1ni1st deterrnine the amperes 0f current which flow in die magnet-coils,mid theref0re the strength of the field-magnet. My device just describedvaries 1she position 0f the brushes 011 the commutator to eause enoughe1eet1ic current to be diverted through the field-magnet coi1s t makethe field-magnet strong enough t0 insure torque enough t0 the armatureto eause it t0 rotate ab approximate1y a constant speed under allvariauions 0'f the load 0n the motor within its capacity f0r work. WVhenthe motor is doing the minimum 0f work, the brushes will have ihepositions of least difierence of potential, the minimum 0f current Willbe diverted th1ough the field-magnet coi1s, and the field-magnet willconsequ ently be very weak. Vhen it is doing the maximum 0f work, thebrushes will be ab the positions 015 greacest difference 0f potential,the maximum current will be diverted through the field-magnet eoils, andthe field-magnet Will b e very streng. The energy absorbed (representedby the 0111ns 1aw formu1a, G R) by the field-magnet coi1s is inproportion t0 the W01k done by the motor. 'lherefore the effieiency ofthe field-magnet is a1ways ab the maximum. Furthermore, the brushes takecontinually the positions coexistent with the then existent true line ofcommutation, beeause their p1oper p0sit-i0ns un- (1e1 varying loads andthe positions they shou1d have under the distortion Of' the magnetie1ines of force fr0m varying relations 0f magnetie strengths 0f armatureand fie1d a1e coincident. Therefore there is 1ittle 01 110 spmking, suchas is so troublesome and destruetive when the brushes are moved in thespeed-government of other motors, especially such as are series-wound.

lt is evident that my speed-governing device may be applied t0 motors ofother 0011- strucoions whenever it is desirable t0 eontrol f01 constaneythe speed of rotation of thei1 armatures by moving the brushes to andfr0m on the eircumferential plane of their commutato1s.

The 1novement 0f brushes in the direction fr01n the plane midway betweenthe p01es and reversely to the direction of rotat-ion of it-s armature,so decrease torque, speed, or both, is applicable t0 series-wound1notors f01' their gevermnent.

I-Iaving described my invention, I c1aim In an electric motor, agovernor of ios speed, Which con'siscs 016 the following parts: a 1'0-tary disk 01 d1um, gripping-weights 011 the disk 01 drunn and movableradially 130 and from, in obedience '00 centrifngal and centripetalforces, a rotatable cylinder concentric With the periphery 0f the disk01 drun1 and gripped by the gripping-weights more 01 less tightly undervariations in he speed 0f rotetion of the disk 01 l1um, brushesimpinging or bearing 0n the commutator of the e1eetric 1110t01 analatoaehed t0 the rotatable cylinder,

and a spring 01 counter-balance attached t0 ehe rotatable cylinder andopposing the roteoion of the rotatable oylinder by the grippingweights.

Signed ab Sai1 Francisco, in the county of San Francisco and State ofCalifo1nia.

NA'1HANIEL SHEPARD KEI'IH. \Vitn esses:

H. J. HYLAND, E. STEVENS.

